Steam-turbine stage



Jan. 1, 1929. 1,697,174

- G. FORNER STEAM TURBINE STAGE Filed Aug. 11, 1924 2 Sheets-Sheet 1Jan. 1, 1929. Y 1,697,174

. s. FORNER STEAM TURBINE STAGE Filed Aug. 11, 1924 2 Sheets-Sheet 2-bjmm n symmwmmnm/a @(QQQK WM (GM (WK K \(xlmmmmit(@m&@iu(u@xmuw@mm(mDDDDJ DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD)DDDDDDDDDDD'QQQQQQQQMMMGQMMQMM(MGGMQMMMQQQQQQQKQQMQQQMMMMGM III Patented Jan. 1,1929.

UNITED STATES GEORG FORNER, OF BERLIN, GERMANY, ASSIGNOR TOAKTIENGESELLSCHAFT BROWN,

1,697,174 PATENT oFFIc BOVERI AND (HE, 012 BADEN, SWITZERLAND.

STEAM-TURBINE STAGE.

Application filedAugust 11, 1924, Serial No. 731,475, and. in GermanyAugust 16, 1923.

This invention relates to improvements in steam turbines of the typewherein the working fluid expands chiefly within the first guide meansor nozzles and the velocity energy and the residual pressure aresubsequently fractionally absorbed by one or more sets of rotor bladesalternating with stationary guide blades. 1

In steam turbines having stepped velocity (Curtis) stages in whichexpansion takes place in the stationary blading, a higher pressureexists in that part of the gap which lies between the active nozzles andthe first row of moving blades than in any other of 1 the gaps orclearances between the stator and rotor. Owing to this higher pressure aportion of the steam issuing from the nozzles leaks into the gap beyondthe nozzle area without doing work. This leakage of 0 steam ma occur inthe radial direction and also in tie direction of rotation. As regardsthe former case, proposals have a ready been made' for reducing theradial leakage. As regards the leakage in the di- 23 rection ofrotation, only the first and the last of the nozzles of-a group that istraversed by the steam come into question.

In the case of the nozzle that is rearmost of a group inthe direction ofrotation, the

so leakage is relatively slight, because in this nozzle the direction ofthe outflow of the steam from the nozzle and thedirection of thedischarging steam leakage are opposed to each other, and because thesurrounding steam which is carried into the gap by the rotation of therotor acts in opposition to the direction of the steam leakage. Thereverse is the case in the foremost nozzle, for which reason the steamleakage is greater 4 in this nozzle. If, as is mostly the case, theCurtis stage is used as the first turbine stage, there is almost alwaysa nozzle regulation employed, so that the number of nozzles that areopen will be different under different conditions of working. Thenozzles may be arranged to be opened in succession by individual valvesfor each nozzle or one valve for a group of nozzles. The last of thenozzles or group of nozzles to be closed by the governor may either bethe foremost nozzle or the rearmost nozzle in the direction of rotation.The maximum advantage of a device for preventing peripheral leakage ofsteam will be obtained when therefore a diminution of the leakage is ofgreater value. In order to best avoid leakage at this point it isadvisable to make the dimensions of the nozzle such that the steam willexpand in it or in the gap wholly or,

almost wholly down to the pressure of the surrounding space. 7

According to the present invention this object is achieved by reducingthe radial height of the nozzle orifice so that its steam can flow,-without becoming through the blades that receive steam from the saidnozzle. Obviously the efficiency of this steam is somewhat diminished ascompared with the eiiiciency of the steam flowing out of the othernozzles.

This drawback is reduced according to the present invention by makingthe exit cross section area of the foremost nozzlesmaller than that ofthe next following nozzle. It is advisable for this purpose to make thecross section such that the steam of the foremost nozzle is able toenter, at most, two blade passages at one and "the same time. This iseffected by making the clear inside exit width of the nozzle, in theperipheral direction, not more than equal to the pitch of the blades. Inmost cases the steam issuing from the foremost nozzle is deflected awayfrom the nozzle axis as the result of the greater degree of expansion.For this reason it is advisable to give a more acute angle to thisnozzle than to the other nozzles, so

as to obtain steam entrance approximately without shock. In certaincases, however, this expedient is not necessary, especially where, evenin the case of a deflected jet of steam, owing to the higherexitvelocity, an entrance takes place approximately without shock. Inthis case, however, the wall between the foremost nozzle and thesecondnozzle should have a thickness such that the congested,

exit jets of the two nozzles will meet only in the immediate vicinity ofthe ent 'ance edge of the blades, so that a disturbing infiuence of thetwo jets upon each other is avoided. V

The accompanying drawings illustrate by way of example one Way ofcarrying the invention into effect.

In the drawings:

Figure 1 represents the outlet openings of a group of nozzles;

Figure 2 represents a section on the line AB of Figure 1;

Figure 3 is a diagrammatic sectional View of a group of nozzles fedthrough a common valve V;

Figure 4 is a view of the exit orifices of the nozzles of Figure 3;

Figure 5 is a diagrammaticsectional view corresponding to that of Figure3 but showing a compound group of nozzles.

Figures 6 and 7 are part sections of Figure 3 on the lines 6-6 and 77respectively.

In the drawings, according to Figure 1 the leading nozzle of the groupis repre sented by S and is made, according to the invention, smaller inits cross section and in its radial dimension than the succeedingnozzles S, S, S. M represents the first row of rotor blades.

Figure 2 shows the discharge angle a of the nozzle S to be more acutethan the corresponding angle a of the nozzles S, S, S.

Figures 8, 4, 6 and 7 represent a nozzle segment or group N suppliedwith steam through a valve V which is controlled by the usual governor.In these figures the leading nozzle orifice S is again smaller in itscross sectional area and in its radial dimension than the other nozzlesS, S, S, and Figure 3 shows the thickening of the rear wall of the firstnozzle S at T, which thickening, in conjunction with the more acutedischarge angle of this first nozzle, causes the proximate edges of thejet from S, and the next jet from S to meet without interferencesubstantially at the entrance edge of the first rotor rim M, and so inthe usual manner through the guide rim G and succeeding rotor rim M Therims M, and M are fixed to the common rotor R, and the guide rim G tothe casing of the turbine.

Figure 5 shows a compound group of nozzles consisting of three groupsfed from a common steam chest through valves V V, and V, respectively.

In this case the action of the governor is arranged to operate on thethree valves V,, V and V in succession, the valve V being the last toclose and the first to open.

The leading nozzle S of the group fed from the valve V, is constructedas hereinbefore described with a smaller cross-sectional area and radialdimension than the remaining nozzles S and is also furnished as inFigure 3 with a thickening T on its rearmost wall.

The advantage of this invention resides in the fact that at the foremostpoint or end of the nozzle segment, where the leakage would be greatestin the case of a higher pressure at the gap, there will take placealmost no discharge of steam into the gap without doing work, and themaintenance of the higher pressure in the gap is thereby assuredprovided that the dimensions of the blades have been correctly chosen.

What I claim is 1. In a turbine, a group of guide nozzles of which theleading nozzle has a discharge orifice of smaller cross sectional areathan those of the other nozzles.

2. In a turbine, a group of guide nozzles of which the leading nozzlehas an outlet orifice of less radial extent than the outlet orifices ofthe other nozzles.

3. In a turbine, a group of guide nozzles of which the leading nozzlehas a discharge orifice of less width in the circumferential directionthan the discharge orifices of the other nozzles.

4. In a turbine, the combination with rotor blading, of a group of guidenozzles of which the leading nozzle has a discharge orifice having awidth not to exceed the pitch of the rotor blading.

5. In a turbine, the combination with a bladed rotor, of a group ofguide nozzles of which the leading nozzle has a smaller discharge areaand a smaller discharge angle than the nozzle posterior to it in thegroup.

6. In a turbine, the combination with a bladed rotor, of a group ofguide nozzles of Which the leading nozzle has a smaller discharge anglethan the adjacent posterior nozzle, said nozzles arranged to directtheir jets to meet without interference substantially at the entranceedge of the rotor bladm F. In a turbine, the combination with a bladedrotor, of a group of guide nozzles of which the leading nozzle has asmaller discharge orifice than the adjacent posterior nozzle, saidnozzles arranged to direct their jets to impinge without interferenceap-' proximately at the entering edge of the.

rotor blading.

8. In a turbine, the combination with a bladed rotor, of a group ofguide nozzles of which the leading nozzle has a smaller dis chargeorifice than the adjacent posterior nozzle, said leading nozzle havingan ex panding discharge throat.

9. In a turbine, the combination with guide nozzles arranged in groups,of valve mechanism for controlling admission of working fluid to thegroups respectively, the admission valve of the leading group being thefirst to open and the last to close, and the leading nozzle of theleading group having a smaller discharge orifice and a smaller dischargeangle than the posterior nozzles of said group.

10. In a steam turbine, the combination with a stage of rotor blading,of a group of nozzles for feeding same, the leading nozzle of the groupbeing constructed to expand the steam passing therethrough down toapproximately the final pressure of the rotor stage.

11. In a steam turbine, the combination with a. stage of rotor blading,of a group of nozzles serving same, the leading nozzle of said groupbeing arranged to deliver steam to the blading stage at approximatelythe exist steam pressure of the stage, said leading nozzle having asmaller discharge angle than the other nozzles of the group, and saidother nozzles being constructed to deliver steam to the blading at apressure higher than its exit pressure from the stage.

In testimony whereof I have signed my name to this specification.

GEORG FORNER.

